Closed grinding circuit



c. ALLEN. CLOSED GRINDING CIRCUIT. APPLIGATION FILED JUNE 10, I920.

Patented Feb. 28, 1922;

2 SHEETSSHEET l- A TTORNE Y c. ALLEN.

CLOSED-GRINDING CIRCUIT.

APPLICATION FILED JUNE 10' 1920.

fl/uzrles Al Len A TTORNE Y Patented Feb. 28, 1922.

2 SHEETS-SHEET 2.

, dewatering.

ABS

CHARLES ALLEN, OF EL PASO, TEXAS.

cLosnn GRINDING clnonrr.

incense.

Specification of Letters Patent.

Patented Feb. 28, 1922- r'lpplication filed June 10, 1920. Serial No. 387,887.

To all whom it may concern. I

Be it known that I, CrrAnLns ALLEN, a citizen of the United States-residing at El Paso, in the county of El Paso and State of Texas, have invented a new and useful Improvement in Closed Grinding Circuits, of which the following is a specification.

This invention relates to closed grinding circuits wherein a classifier, dewaterer or the like is used in combination with a pulverizer.

The object is to improve the efliciency of such a grinding circuit. In carrying out this object, I arrange in combination an automatically controlled spigot discharge classifier or dewatcrer in position to deliver its classified product to a pulverizer, and an air-lift to receive the material from the pulverizer and return it to. the classifier or dewaterer.

Solids fed to ball mills or tube mills should be accompanied by only a small quantity of water, approximately 30% water to 70% solids by weight. All feed streams that will freely flow down launders must be dewatered or partially dewatered before entering the mill, and effective hydraulic classification is impossible when the feed stream is composed of 30% water and 70% solids. Therefore, water must be added to the ball mill dischar e for classification purposes and the partic es to be reground must be delivered to the ball mill in a dewatered condition. The efliciency of the pulverizer very largely depends upon the perfectness and uniformity of the classification and the y the present invention, I am enabled to meet these conditions exactly regardless of fluctuations in the character or in the volume in the primary feed.

In the accompanying drawings, Fig. 1 shows a vertlcal central sectiona view of the combination constituting the present invention and employing a preferred type of classifier.

Fig. 2 shows a similar view of the combinatlon employing a classifier or sand trap. In the drawings, I show a ball mill with a primary feed spout or launder 11; The mill discharges at 12 into a well 13 which is supplied with water from a valved pipe 14. Extending from the bottom of the well to a point above the ball mill is an air-lift tube 15 arranged at the upper end of which is a receptacle 16, including a deflector 17 overlying. the upper end of the airlift tube and spaced therefrom. Within the tube 15 is a compressed air-pipe 18 extending from an outside source of supply downwardly within the tube 15 to a point near the bottom of the latter where the said tube 15 is flared outwardly and is provided with perforations or apertures 15 to admit material from the well to the interior of'the tube.

Air under pressure discharge from the pipe 18 will lift the material in the tube 15 and discharge it into the receptacle 16, the deflector 17 preventing the material from being blown out of the receptacle. From the receptacle 16 the material .passes into a launder 18 which communicates with a classifier or dewaterer.

As shown in Fig. l, the classifier or dewaterer is in the form of a cone 2O havin a bottom discharge orifice controlled by a valve 21'. This valve 21 is automatically actuated by connections 22 with a float 23, which float is arranged near the top of the tank surrounding a feed spout orpipe 24 into which spout or pipe the material from the launder 18' passes.

Material enters the tank from the launder 18 and the lighter and more slowly settling particles will overflow the rim of said tank and pass out through a discharge spout 25 into a discharge launder 26. The heavier and more quickly settling particles will accumulate in the bottom of the tank, it being understood that the valve 21 is normally held in closed position by the weight of the float 23. When the accumulated material in the tank reaches a predetermined density, the float 23 will be raised, thereby opening the valve 21 and allowing the settled material to escape. The classifier is arranged above the feed launder 11 and the material discharged through the spigot of said classifier enters the ball mill through said feed launder where it is reground and discharged again into the well 13.

In Fig. 2, I show an automatic sand trap in place of the classifier just described. It

material enters the tank through the launder 18 as in the case of Fig. 1 and the lighter product overflows the rim of the tank or passes out through a spout36 into a discharge launder 37, while the heavier product accumulates in the bottom of the tank until the weight thereof causes the tank to be lowered depressing the springs and opening the discharge orifice 32, whereupon the product to be further comminuted will'tpass out into the primary feed launder '11, as in the case of Fig. l.

The uniform percentage of water to solids in the spigot discharge of the automatic classifier is due to the continuous maintenance of settled solids in that portion of the tank overlying the discharge orifice. The discharge closely approximates 30% water to 70% solids when the solids are 2.6-1 specific gravity and as these percentages are automatically continuously. maintained, the automatic classifier is peculiarlyadapted to closed circuit grinding. Without automatic control of the area of the spigot outlet such results are unobtainable.

A given area of spigot orifice is the correct area for a certain volume and character of discharge only. If the quantity of solids that should be discharged through the spigot orifice increases in the feed stream, the result is the filling up of th classifier, and the overflowing of particles that should have been discharged through the spigot for further comminution, and when the quantity of solids that should be discharged through the spigot orifice diminishes in the feed stream, then particles that should overflow the classifier are discharged through the spigot and if this condition prevails for a short time, the classifier is emptied of settled particles. Hence, the advantage of the automatic control of the spigot orifice.

arious changes in the construction and arrangement of the several parts may be employed without departing from the spirit of my invention as disclosed in the appended claims.

Havin thus described my invention,

what I c aim and desire to secure by Letters overflow for light and slowly settling. particles and a bottom discharge orifice for quickly settling and heavy particles, means actuated by changes in the density of the material in the vessel .for controlling said bottom dischar e orifice, and means to return the classi ed and dewatered material to the pulverizer.

2. A closed grinding circuit including a pulverizer, an elevator into which the pulverized material discharges, a classifying and dewatering vessel to receive the material from the elevator, said vessel having a rim overflow for light and slowly settling particles and a bottom discharge orifice for quickly settling and heavyparticles, a valve to control the bottom discharge orifice, a float within the vessel responsive to changes in the densit and open t e valve when such material reaches a predetermined density, and means to return the classified and dewatered material to the pulverizer.

CHARLES ALLEN. A

Witnesses:

A. H. SWETT, J. L. ELY.

of the material within to rise 

